Conventionally, there are known hybrid construction machines such as the one disclosed in Patent Literature 1 which include an engine, an electric storage device, a generator for generating an electric power by a power of the engine, an actuator to be operated by a power of the engine (an electric power of the generator) and an electric power of the electric storage device, and an electric power control device for determining the allocations of an electric power necessary for the actuator between the electric storage device and the generator.
The electric power control device disclosed in Patent Literature 1 determines the electric power allocations so that the output of the engine falls within a predetermined engine output control range defined by an upper limit value and a lower limit value (by an upper limit electric power and a lower limit electric power of the generator).
Specifically, when the necessary power (electric power) for the engine is smaller than the lower limit value (the generator power lower limit value), a surplus electric power generated by the generator is charged in the electric storage device. On the other hand, when the necessary power is greater than the upper limit value (the generator power upper limit value), an electric power from the electric storage device is supplied to the actuator in addition to an electric power generated by the generator (to assist the engine while supplementing a power of the actuator).
Here, works performed by a hybrid construction machine include those performed in a relatively short period of time (for example, a dumping work using a working attachment) and those performed in a relatively long period of time (for example, a continuous (ascending) travelling and a pressing work using a working attachment).
During the work that is performed in a long period of time, a state that the necessary power for the engine exceeds the upper limit value of the engine output (the state will be hereinafter referred to as “high load state”) is likely to continue for a long time.
However, in the electric regulator disclosed in Patent Literature 1, when the high load state continues for a long time, an assist provided by an electric power of the electric storage device continues for a long time, which results in a decrease of the charged rate of the electric storage device. This has been a problem.
The decrease of the charged rate of the electric storage device may cause lack of a necessary electric power during a regular control after the high load state ends.